The Hough transform is a technique which can be used to isolate features of a particular shape within an image. Because it requires that the desired features be specified in some parametric form, the classical Hough transform is most commonly used for the detection of regular curves such as lines, circles, ellipses, etc. A generalized Hough transform can be employed in applications where a simple analytic description of a feature(s) is not possible.

Some Examples [FIX IMAGES & UPLOAD]Squidfingers ( www.squidfingers.com/patterns) has a repository of 140-odd pixel patterns in GIF format, from the modern to the arabesque.